In this example, we should not report all the digits from the final calculation. By including all the numbers we imply that we were able to measure the dimensions with greater precision than actually possible with a standard inch ruler. We should round and report the diagonal calculation with two significant figures since the length and width values were given with two significant figures. If we round off in the middle of our calculation and square root 190, we will be removing valuable information that would otherwise provide a more accurate diagonal value. By rounding down midway we end up with a value that is less than the true diagonal value. You could argue that we are going to report our final answer with two significant figures anyway and end up at the same number, but it is a bad habit that can lead to unreliable data in other situations.